An increasing number of Americans have insufficient levels of vitamin D, according to a new report.

Scientists from the University of Colorado have found that the average blood levels of vitamin D appear to have decreased in the U.S. between 1994 and 2004.

They suggest that in addition to poor diet, a decline in outdoor physical activities and more successful campaigns to reduce sun exposure may have contributed to this phenomenon.

They also believe the currently recommended doses – 200 international units per day from birth to age 50, 400 IUD from age 51 to 70 and 600 IUD for adults age 71 and older – focus mainly on improving bone health.

“Current recommendations for dosage of vitamin D supplements are inadequate to address this growing epidemic,” the researchers write in the March 23 issue of Archives of Internal Medicine .

“Increased intake of vitamin D (1,000 IUD or more) particularly during the winter months and at higher latitudes would improve vitamin D status and likely improve the overall health of the U.S. population.”

Clinicians now believe that insufficient levels of vitamin D are not only associated with rickets and other bone problems in children, but they have also been linked to mature-age disorders such as heart disease and certain types of cancer.

Those who are concerned that they do not get a sufficient amount of vitamin D from their diet may consider turning to nutritional supplements.